1. Field of the Invention
The present invention relates to a control device for a die cushion mechanism.
2. Description of the Related Art
In a press machine for effecting press-work such as bending, drawing or punching, it is a known practice to install a die cushion mechanism as an accessory unit for applying a predetermined force (pressure), from the side of a support member (usually called bolster) that supports a second mold to a movable support member (usually called slide) that supports a first mold used for the press-work, during the machining operation. The die cushion mechanism is usually so constituted that a cushion pad moves together with a slide while applying a force (pressure) to the slide after the slide (or the first mold) moving in a direction of closing the mold is brought into direct or indirect collision with a moving element (called cushion pad) held with a predetermined pressure until when the mold is opened after the mold is closed (molding). During this period, the peripheral region of a working portion of a workpiece is held between the cushion pad and the slide to prevent the occurrence of wrinkles on the workpiece.
The die cushion mechanism is operated by a control device. The control device produces an instruction related to the velocity of the die cushion mechanism and an instruction related to the velocity of the slide. The die cushion mechanism and the slide are driven based on these instructions (see, for example, Japanese Patent Application No. 2005-195097).
However, the above conventional control device forms the instruction related to the velocity of the die cushion without referring to any reference for judgement. When the velocity command that is produced for the die cushion mechanism is relatively small, therefore, the relative velocity between the die cushion and the slide becomes relatively great. As a result, the slide comes into collision with the die cushion at a relatively large velocity and produces large noise on collision. In this case, further, a relatively large impact acts on the first and second molds causing their life to be shortened.
In order to suppress the noise and the impact, therefore, it can be considered to decrease the relative velocity between the die cushion and the slide. In this case, however, though the noise can be suppressed, as a pressure acting on the workpiece from the first and second molds is decreased, and it is possible that the workpiece is not worked to a sufficient degree.
It is therefore desired to obtain an optimum velocity for the die cushion to suppress the noise while favorably working the workpiece. From the same reason, further, it is desired to obtain an optimum velocity for the slide.
The present invention was accomplished in view of the above circumstances, and has an object of providing a control device capable of forming an optimum velocity command for the die cushion and/or an optimum velocity command for the slide.